1. Field
The present disclosure relates to semiconductor devices and methods of manufacturing the same, and more particularly, to gallium nitride based semiconductor devices and methods of manufacturing the same.
2. Description of the Related Art
Recently, along with rapid developments in information and communication technologies, technologies for high-speed and massive-capacity signal transmission are being rapidly developed. In this regard, with an increasing demand for personal mobile phones, satellite communications, military radars, broadcasting communications, and communication relay devices, there has been an increasing request for high-speed and high-power electronic devices which are required for high-speed telecommunication systems using microwave and millimetric wave bands. Power devices for controlling relatively high levels of power are used for various purposes in many fields including communication fields, and various types of research are being conducted thereon.
A gallium nitride (GaN) based semiconductor has excellent material properties, such as a large energy gap, high thermal and chemical stability, high electron saturation speed (˜3×107 cm/sec), etc., and thus a GaN-based semiconductor may be applied not only to an optical device, but also a high frequency and high power electronic device. An electronic device employing a GaN-based semiconductor has various advantages, such as a high breakdown electric field (˜3×106V/cm), high maximum current density, stable operation characteristics at high temperatures, high thermal conductivity, etc. In particular, in the case of a heterostructure field effect transistor (HFET) employing a GaN-based heterojunction structure, since band-discontinuity at a junction interface is large, electrons may be densely concentrated at the junction interface, and thus electron mobility may be further increased. Due to such a material property, a GaN-based semiconductor may be applied to a high power device.
However, since a GaN-based semiconductor device generally employs a sapphire substrate having relatively low thermal conductivity, a GaN-based semiconductor device does not have an excellent heat dissipation characteristic. Although a SiC substrate may be used instead of a sapphire substrate for an improved heat dissipation characteristic, a SiC substrate is relatively expensive (about 10 times more expensive than a sapphire substrate), and thus the overall cost for manufacturing a GaN-based semiconductor device increases. Furthermore, in the case of using a GaN-based semiconductor device as a power device, there are various problems which are related to a voltage withstanding characteristic, manufacturing processes, etc.